An Introduction to Cosmology and Particle Physics

The following sections are included:

• FOREWORD

• CONTENTS

The purpose of Physical Cosmology is to study the universe from a global point of view and to describe the physical processes which have occurred throughout its evolution and which have observable consequences nowadays…

The standard cosmological model is determined once the present values of the Hubble constant, H_o, the deceleration parameter, q_o (or the density parameter Ω_o), the temperature of the cosmic microwave background radiation , T₀, the baryon-to-photon number ratio, η_o, and the number of light neutrino families, N_v, are specified.

In this Chapter the most important methods used to measure H_o, q_o and Ω_o are considered. In forthcoming Chapters, the derivation of the T_o, η_o and N_v parameters will be discussed.

As explained in Chapter 1, the dynamical evolution of the universe is characterized by an expansion which results in a decrease of the temperature of the cosmic constituents. Below T ⋍ 1 MeV, the cosmic gas consists of photons and electron and baryon traces which are in thermal equilibrium with the radiation until the temperature reaches a value T_R ⋍ 4000 K, and decoupled neutrinos at “temperature” T_v. When T < T_R, electrons and nuclei recombine forming neutral atoms. Then matter becomes transparent to radiation and the thermal contact between these components is lost…

In the preceding Chapters it was emphasized that the standard Friedmann-Robertson-Walker (FRW) cosmologies explain, in rather a natural way, the Hubble law and the microwave background of thermal radiation at 2.7 K. In the present Chapter we will discuss a new piece of evidence in support of the big-bang model: the consistency between theory and observations in regard to the abundances of the light elements D, ³He, ⁴He and ⁷Li…

The problem of the origins of the large scale structure of the universe as observed today is an unsolved one. The standard framework to understand it rests on the hypothesis that it has been formed from quantum fluctuations originated at very high temperatures. These fluctuations evolved in a linear regime until they reached a nonlinear regime at relatively small scales, and then they collapsed giving rise to the bound objects, or to the looser structures we observe nowadays…

In order to test out some parameters of elementary particles, the early universe proves to be the most efficient accelerator. In this Chapter some observable effects of the presence and decay of exotic particles in the early universe will be considered. Limits on their parameters (mass, lifetime, abundance, etc.) can be derived by comparing the magnitude of these effects with astronomical data.

Most of cosmological applications of field theories are based upon the theory of phase transitions^(l). In particular the concept of spontaneous symmetry breaking in gauge theories⁽²⁾ and symmetry restoration^(l) at high temperatures will play a fundamental role. In this Chapter we will introduce Green functions in Quantum Field Theory at finite temperature^(3,4) and compute the corresponding one-loop effective potential in a general renormalizable theory. We will illustrate the notion of phase transition with a few simple examples, including a popular SU(5) model broken by radiative corrections. We will assume the reader familiar with the methods used in Quantum Field Theory at zero temperature to compute the effective potential⁽⁵⁾. Also a suitable background on Grand Unified Theories⁽⁶⁾ would be welcome.

The following sections are included:

• INTRODUCTION

• THE FLATNESS (OLDNESS) PROBLEM

• THE HORIZON PROBLEM

• A SOLUTION TO THE FLATNESS AND HORIZON PROBLEMS: INFLATIONARY UNIVERSE SCENARIOS
  • INFLATION SOLVES THE HORIZON PROBLEM
  • INFLATION SOLVES THE FLATNESS PROBLEM

• OTHER PROBLEMS OF THE STANDARD COSMOLOGICAL MODEL
  • SMALL-SCALE INHOMOGENEITY AND GALAXY FORMATION
  • THE DOMAIN WALL PROBLEM
  • THE BARYON NUMBER OF THE UNIVERSE
  • THE COSMOLOGICAL CONSTANT PROBLEM

• BARYOGENESIS
  • THE STANDARD OUT-OF-EQUILIBRIUM DECAY SCENARIO
  • BARYOGENESIS IN GRAND UNIFIED THEORIES

• REFERENCES

The following sections are included:

• INTRODUCTION

• THE HAWKING TEMPERATURE

• THE DYNAMICS OF FIRST-ORDER PHASE TRANSITIONS
  • SEMICLASSICAL THEORY OF FALSE VACUUM DECAY
  • GRAVITATIONAL EFFECTS ON FALSE VACUUM DECAY
  • THE HAWKING-MOSS TRANSITION

• THE SLOW ROLLOVER REGIME

• COHERENT FIELD OSCILLATIONS AND REHEATING

• ENERGY DENSITY PERTURBATIONS AND GALAXY FORMATION

• REFERENCES

The following sections are included:

• NEARLY COLEMAN-WEINBERG MODELS

• INFLATION CRIES OUT FOR SUPERSYMMETRY

• PRIMORDIAL INFLATION IN SUPERGRAVITY
  • INFLATIONARY MODELS IN MINIMAL SUPERGRAVITY
  • INFLATIONARY MODELS IN NO-SCALE SUPERGRAVITY

• CHAOTIC INFLATION

• DOUBLE INFLATION

• REFERENCES

The following sections are included:

• APPENDIX
  • CONVERSION FACTORS IN NATURAL UNITS (h = c = K_B = 1) AND SOME COSMOLOGICAL CONSTANTS
  • REFERENCES